To reduce the deterioration of image quality due to image compression processing by selecting a quantization coefficient matched with the color components of an input image.

A color-space conversion part 201 converts target image data (RGB image signal) into a luminance color difference signal, a color component ratio calculation part 202 calculates the ratio of respective color components of the target image data by using the obtained luminance color difference signal, a quantization coefficient selection part 203 selects a quantization coefficient matched with the target image data on the basis of the calculated ratio of respective color component, and a quantization part 205 quantizes the DCT coefficient of the target image data by using the selected quantization coefficient.